In the course of our research on blood imaging (as distinguished from flow imaging) we have devised a system for measuring and/or imaging oxygen saturation in vessels. Our initial results using both in vitro and in vivo studies appear very encouraging. Oxygen saturation could well provide the most significant functional MR image. We acquire data with this technique in normal imaging times and with typical spatial resolution. We anticipate a wide range of clinical applications. In addition to optimizing and clinically verifying this technique, we plan to study the same effect to estimate the oxygen level in organs and tissue capillary beds.